Four years after the 2007 slayings of Christopher Horton, 16, and Brian Dean, 20, detectives had little to go on.

No suspects. No sign of the gun used to shoot the pair. No witnesses to the shooting outside a house where officers found Horton sprawled next to a trash can and Dean on the front porch.

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In 2011, the case was reassigned to a detective who later came across what he considered a compelling piece of evidence: a YouTube video of Antwain Steward, a local rapper with the stage name Twain Gotti, performing his song “Ride Out.”

Steward denies any role in the killings, but the authorities took the lyrics to be a boast that he was responsible and, based largely on the song, charged him last July with the crimes.

His case is one of more than three dozen prosecutions in the past two years in which rap lyrics have played prominent roles. The proliferation of cases has alarmed many scholars and defense lawyers, who say that independent of a defendant’s guilt or innocence, the lyrics are being unfairly used to prejudice judges and jurors who have little understanding that, for all its glorification of violence, gangsta rappers are often people who have assumed over-the-top and fictional personas.

“If you aspire to be a gangsta rapper, by definition your lyrics need to be violent,” said Charis Kubrin, an associate professor of criminology, law and society at the University of California, Irvine.

Important tool?

Prosecutors say the lyrics are an important tool for battling criminals who use an outspoken embrace of violence as a weapon of control. “Just because you put your confession to music doesn’t give you a free pass,” said Alan Jackson, a former senior prosecutor in the Los Angeles County District Attorney’s Office.

In some of the cases, police say, the lyrics represent confessions. More often, the lyrics are used to paint an unsavory picture of a defendant to help establish motive and intent. Increasingly, the act of writing the lyrics is being prosecuted because prosecutors contend that the words amount to a criminal threat.

The debate is playing out in courtrooms across the country. In Topeka, Kan., a judge is expected to rule in coming months on a motion to exclude rap lyrics from a double-homicide case. The New Jersey Supreme Court will soon hear arguments on whether 13 pages of lyrics written by Vonte Skinner — including lines such as “four slugs drillin’ your cheek to blow your face off and leave your brain caved in the street” — should have been admitted at his trial for attempted murder.

In Virginia, Steward is to go on trial in May.

“What’s getting really unnerving,” said Erik Nielson, an assistant professor of liberal arts at the University of Richmond, “is the amount of time it appears both police and prosecutors are spending over rap lyrics and videos on social media rather than using that time to go and gather more convincing, more conventional forms of evidence.”

Most rappers charged in recent cases have been amateur performers who aspire to fame, even though gangsta rap is no longer as popular as it was.

Critics like Andrea Dennis, an associate professor of law at the University of Georgia, say law enforcement ignores the fact that rappers do not necessarily live the lives they sing about.

Rick Ross, for example, took his stage name from a West Coast drug kingpin of the 1980s, Freeway Rick Ross. When he broke through as a performer in 2006, his street-wise image and rhymes about the Miami gangster lifestyle seemed like references to a shady past. In reality, he had once been a corrections officer.

Those who oppose the use of the lyrics say prosecutors have singled out rap as a literal evocation of reality when the lyrics in other musical genres have long been acknowledged as fictional.

A brief filed in the Skinner case by the New Jersey chapter of the ACLU turns to “Crime and Punishment” and “Folsom Prison Blues” to make a similar point. “That a rap artist wrote lyrics seemingly embracing the world of violence is no more reason to ascribe to him a motive and intent to commit violent acts than to saddle Dostoevsky with Raskolnikov’s motives or to indict Johnny Cash for having ‘shot a man in Reno just to watch him die.’”

First Amendment

In a relatively new twist, rap lyrics themselves are viewed as the wrongdoing in several cases.

Last month, two men in Pittsburgh, Rashee Beasley and Jamal Knox, were sentenced to prison after posting a rap video that threatened to kill two police officers who had arrested them on firearms violations. Although they argued that they never intended to hurt the officers and that the video was protected speech, they were convicted of intimidation, terrorist threats and other charges.

“It is abundantly clear to me that the conduct of the defendants here is not protected by the First Amendment, because it far exceeds what the First Amendment allows,” said Judge Jeffrey Manning of the Allegheny County Court of Common Pleas.

Some lawyers argue that rap music is protected artistic expression, just like novels and films. They say the courts should apply stringent standards before allowing such lyrics into evidence, in part because of the chilling effect on free speech.

“Our point is there should be heightened scrutiny,” said Ezra Rosenberg, a lawyer who filed the brief for the ACLU in the Skinner case. “Just because it rhymes and has a beat doesn’t necessarily make it art. But you have to be particularly careful.”

That view does not carry weight with Jackson, the former Los Angeles prosecutor.

“We’re not stepping on the First Amendment,” he said. “We’re not preventing you from writing.”

Before he was arrested last summer, Steward, 22, had been making a name for himself. Rapping as Twain Gotti, he had released six mixtapes, performed at clubs along the East Coast and landed with a New York management firm.

He was about to embark on a 22-city tour when the police charged him with the Horton and Dean slayings from six years earlier, when he was 16.

Witnesses told police Steward had been bested in a street fight by Horton, a supposed rival gang member. Relatives of Horton’s also steered investigators to a YouTube video of Twain Gotti’s song “Ride Out.”

Steward’s lawyer, James Ellenson, said the song appeared to be a significant part of the prosecution’s case, because there were no witnesses to the shooting and other evidence is problematic. The prosecution declined to comment.

Steward denies being a gang leader or fighting with one of the victims. And the lyrics don’t neatly correspond to the crime: No knife was involved, the song mentions only one slaying, and shell casings found at the scene were of different calibers from the gun cited in the song.

In an interview in jail, not far from the housing project where he grew up, Steward said his songs should not be taken literally. “I speak for the people who come from a bad place, you feel me,” he said. “It’s not about me. It’s about where I’m from.”